1. Field of the Invention
This invention relates to an impact damper having two tubes slidable one about the other such that one of the tubes can be pushed into the other tube. In particular, such an impact damper is used in a motor vehicle to slow down the motor vehicle upon collision of the motor vehicle with an obstacle. Such an impact damper works by means of hydraulic damping forces and pneumatic spring forces. The inner tube of the impact damper is closed by a bottom, or base, and essentially contains, in sequence starting from the bottom, a gas chamber which holds a gas cushion at high pressure, a separating piston guided tightly and movably within the inner tube, a first fluid chamber, a partition defined within the inner tube and having a throttle opening, a second fluid chamber in communication with the first fluid chamber via the throttle opening, and a work piston which is connected via a piston rod to the outer tube, which outer tube is slidably movable and guided about the inner tube.
2. Background of the Invention
Known impact dampers, for example, the impact damper as disclosed by DE-PS 34 19 165, which corresponds to U.S. Pat. No. 4,641,872, generally can have two tubes which are slidably movable one inside of the other. Of the two tubes, the sealed inner tube of the impact damper of DE-PS 34 19 165 includes, in sequence starting from the bottom, a gas chamber containing a high pressure gas cushion, a separating piston guided so that it can move in a sealed manner within the inner tube, and a first fluid chamber connected via a throttle to a second fluid chamber. The first fluid chamber being used to generate hydraulic damping forces. With such an impact damper, the maximum stroke of the piston is essentially large enough to absorb the energy of a collision impact at vehicle speeds of up to about 8 km/h. The expansion equalization and the return of the impact damper into its base position is accomplished by means of the gas cushion which is contained in the closed gas chamber.